Generally, a construction machine such as a hydraulic excavator has a construction wherein it includes, for example, as shown in FIG. 14, an upper revolving unit 100 with an operator cab (cabin) 600 provided on a lower traveling body 500 having caterpillar members 500A, and further, a joint type arm mechanism composed of a boom 200, a stick 300 and a bucket 400 is provided on the upper revolving unit 100.
And, based on extension/contraction displacement information of the boom 200, stick 300 and bucket 400 obtained by stroke sensors 210, 220, 230 and so forth, the boom 200, stick 300 and bucket 400 can be driven suitably by hydraulic cylinders 120, 121 and 122, respectively, to perform an excavating operation while keeping the advancing direction of the bucket 400 or the posture of the bucket 400 fixed so that control of the position and the posture of a working member such as the bucket 400 can be performed accurately and stably.
It is to be noted that the hydraulic cylinders 120 to 122 are operated by operation levers (not shown) normally provided in the operator cab 600.
By the way, a semiautomatic control system for such a construction machine as described above has been proposed wherein the boom 200, stick 300, bucket 400 and so forth are set so that they may perform a sequence of operations set in advance and the hydraulic cylinders 120, 121 and 122 are controlled individually so that their operations set in this manner may be performed.
Here, as the semiautomatic control mode described above, a bucket angle control mode in which the angle (bucket angle) of the bucket 400 with respect to a horizontal direction (vertical direction) is always kept fixed even if the stick 300 and the boom 200 are moved, a slope face excavation mode (bucket tip linear excavation mode or raking mode) in which a tip 112 of the bucket 400 moves linearly, and so forth are available.
By the way, in such semiconductor control modes as described above, the operation levers for controlling the operations of the hydraulic cylinders 120 to 122 function as members for setting target moving velocities for the stick 300 and the boom 200.
In particular, in a semiautomatic control mode, the moving speeds of the stick 300 and the boom 200 are determined in response to operation amounts of the operation levers.
However, a semiautomatic system applied to a conventional construction machine has such various subjects as given below.
(1) If an operator operates an operation lever suddenly upon starting of working in a semiautomatic control mode, then control instruction values to the hydraulic cylinders 120 to 122 of the boom 200, stick 300 and bucket 400 vary instantly, and it is considered that the load may be applied suddenly to the hydraulic cylinders 120, 121 and 122. In this instance, there is the possibility that the hydraulic cylinder 120, 121 or 122 may not operate smoothly but operate while accompanying a light impact, vibrations, a shock or the like, and further, there is the possibility that the accuracy of the locus of the bucket tip position may be deteriorated.
In order to eliminate such a situation as described above, it is a possible idea to increase the moving velocity of the bucket tip gradually (ramp up process) or give a smooth velocity variation through a low-pass filter even if an operation lever is operated suddenly. However, in a semiautomatic control mode, since control signals to the hydraulic cylinders are fed-back information obtained by time differentiating the cylinder positions, even if such a ramp up process as mentioned above or the like is performed, the instruction values to the hydraulic cylinders vary discontinuously depending upon the time differentiation information of the cylinder positions. Consequently, there still is a subject that the boom, stick or bucket does not operate smoothly.
(2) In semiautomatic control, where an operation (horizontal leveling operation or the like) wherein the bucket tip position is moved linearly is to be performed in a slope face excavation mode, it is supposed that the loads to the hydraulic cylinders 120 to 122 during an excavation operation may be varied by the shape of the ground, the excavation amount or the like, and in such a case, where conventional PID control is employed, there is the possibility that the degrees of positioning accuracy of the hydraulic cylinders 120 to 122 or the degree of accuracy of the locus of the bucket tip position may be deteriorated.
Further, where feedback control is performed for the hydraulic cylinders 120 to 122, it is supposed that variations of the dynamic characteristics of control objects (for example, the hydraulic cylinders 120 to 122 or solenoid valves provided in hydraulic circuits) arising from a temperature variation of operating oil have an influence on the control performances of closed loops, resulting in deterioration of the stability of the control system.
In order to eliminate such a situation as described above, the control gains of the closed loops should be reduced to increase the gain margins or the phase margins. However, there is a subject that this results in deterioration of the degrees of positioning accuracy of the hydraulic cylinders 120 to 122 or of the degree of accuracy of the locus of the bucket tip position.
(3) Where, in a semiautomatic control mode, the boom 200, stick 300 and bucket 400 are locus controlled (tracking controlled) by feedback control, since the instruction values to the cylinders 120 to 122 are calculated based on deviations of the feedback (that is, control errors between input information and output information), it is difficult to reduce the deviations during operation of the cylinders to zero, and as a result, the bucket tip position sometimes exhibits an error from a target value.
In short, in such feedback control, since actual cylinder positions or cylinder velocities are detected and compared with target cylinder positions or target cylinder velocities and control is performed so that the deviations between them may approach zero, it is difficult to eliminate the deviations completely during control, and there is a subject that a control error is caused thereby.
(4) Where such an operation as to, for example, level the ground (slope face formation) is to be performed, an operation of linearly moving the tip of the bucket 400 (that is, the stick 300) is required. However, according to the prior art, since the boom 200 and the stick 300 are controlled independently of each other by the hydraulic cylinders 120 and 121, respectively, it is very difficult to finish a slope face with a high degree of accuracy.
In particular, where the boom 200 and the stick 300 are electrically feedback controlled using solenoid valves or the like as described above, if the corresponding hydraulic cylinders 120 and 121 are controlled independently of each other, respectively, then even if the respective feedback control deviations are small, the control deviations cannot be ignored depending upon the positions (postures) of the boom 200 and the stick 300, and an error from a target tip position (control target value) of the bucket 400 sometimes becomes very large.
For example, if control of the boom 200 is delayed with respect to the stick 300 due to the control deviations described above when the bucket 400 is at a position at which a slope face is to be formed subsequently, then the tip of the bucket 400 will bite into the ground, but if control of the stick 300 is delayed with respect to the boom 200, then the bucket 400 will operate while it remains floating in the air.
In this manner, there is a subject that, if the boom 200 and the stick 300 are individually controlled fully independently of each other, then it is very difficult to operate the boom 200 and the stick 300 while maintaining control target values.
(5) Where an operation of moving the tip of the bucket 400 linearly (called bucket tip linear excavation mode) such as horizontal leveling of the ground (slope face formation) is required, with the conventional control apparatus for a hydraulic excavator, the operation is realized by feedback controlling the boom 200 (hydraulic cylinder 120) and the stick 300 (hydraulic cylinder 121) electrically independently of each other. However, since the hydraulic cylinders 120 and 121 are feedback controlled independently of each other based on control target values obtained from a target bucket tip position, for example, when it is tried to pull the stick 300 from a condition wherein the bucket 400 is positioned far from the construction machine body 100 toward the construction machine body 100 side to linearly move the tip of the bucket 400, if the position deviation of the boom 200 is small (the delay is little) and the position deviation of the stick 300 is large (the delay is much), then the actual tip position of the bucket 400 is displaced upwardly from the target position (target slope face). As a result, there is a subject that the finish accuracy of the slope face is deteriorated very much.
(6) Where an operation (raking) of linearly moving the tip of the bucket 400 as in, for example, a horizontal leveling operation is performed automatically by a controller, solenoid valves (control valve mechanisms) in the hydraulic circuits for supplying and discharging operating oil to and from the hydraulic cylinders 120, 121 and 122 are electrically PID feedback controlled to control extension/contraction operations of the hydraulic cylinders 120, 121 and 122 to control the postures of the boom 200, stick 300 and bucket 400. However, in the hydraulic circuits which control the extension/contraction operations of the hydraulic cylinders 120, 121 and 122, operating oil pressures are produced by pumps which are driven by an engine (prime mover), and if the rotational speed of the engine is varied by an external load or the like then, then also the rotational speeds of the pumps are varied by the variation, resulting in variation of the discharges (delivery capacities) of the pumps. Consequently, even if the instruction values (electric currents) to the solenoid valves are equal, the extension/contraction velocities of the hydraulic cylinders 120, 121 and 122 are varied. As a result, the posture control accuracy of the bucket 400 is deteriorated, and the finish accuracy of a horizontally leveled face or the like by the bucket 400 is deteriorated.
Thus, it is a possible idea to use, in order to cope with such a rotational speed variation of the engine as described above, a pump of the variable discharge type (variable delivery pressure type, variable capacity type) for the pumps and adjust the tilt angles of the pumps to control the pumps so that the delivery capacities of the pumps may be fixed even if the rotational speed of the engine (that is, the rotational speeds of the pumps) varies. However, since such tilt angle control is slow in response, there is a subject that target cylinder extension/contraction velocities cannot be secured and deterioration of the finish accuracy cannot be avoided.
(7) With the prior art wherein a circuit of the open center type is used for the hydraulic circuits, for example, where the excavation load is extremely heavy, as the load increases, the oil pressures of the boom 200 (hydraulic cylinder 120) and the stick 300 (hydraulic cylinder 121) rise and the extension/contraction displacement velocities of the hydraulic cylinders 120 and 121 drop, and finally, the operations of the boom 200 and the stick 300 (that is, the operation of the bucket tip) sometimes stop.
In this instance, with the PID feedback control system, since the velocity information (P) of the bucket tip becomes equal to zero and the position information (D) is fixed to a value equal to that upon stopping of the stick, they have no influence on target velocities for the extension/contraction displacement velocities of the hydraulic cylinders 120 and 121 which are based on the information (proportional operation factors), but since I (an integration factor) is involved in the control system, the target velocities of the hydraulic cylinders 120 and 121 resultantly continue to increase.
Accordingly, if, for example, a rock under excavation which has been caught by the bucket tip breaks in this condition and the load is removed suddenly from the boom 200 and the stick 300, then the hydraulic cylinders 121 and 122 will suddenly begin to move at velocities much higher than their target velocities. As a result, there is a subject that the finish accuracy of an excavation operation is deteriorated significantly.
(8) Where such control that the angle (bucket angle) of the bucket 400 with respect to the horizontal direction (vertical direction) is always kept fixed even if the boom 200 and the stick 300 are moved such as where excavated sand and earth or the like are conveyed while they are accommodated in the bucket 400, with the PID feedback control system for the bucket 400 (hydraulic cylinder 122), if the deviation between the actual bucket angle and the target bucket angle becomes large during operation of the boom 200 and/or the stick 300, then the instruction value (control target value) to the hydraulic cylinder 122 is increased to decrease the deviation by an action of the I (integration factor) of the P (proportion factor), I (integration factor) and D (differentiation factor). However, when the operation levers (operation members) 6 and 8 for the boom 200, stick 300 and bucket 400 are moved to their neutral positions (inoperative positions) to stop the bucket 400, since the instruction value to the hydraulic cylinder 122 is not reduced to zero immediately due to an accumulation amount of the I (integration factor) till the stopping time. Consequently, there is a subject that, even if the operation levers 6 and 8 are moved to the inoperative positions, the bucket 400 does not stop immediately and an overshoot occurs, resulting in deterioration of the control accuracy.
The present invention has been made in view of such various subjects as described above, and it is an object of the present invention to provide a control apparatus for a construction machine having a semiautomatic control mode which achieves further augmentation of functions.